Reference

Clinical trials glossary

Plain procedural definitions for fields and terms you may encounter on ClinicalTrials.gov and in this directory. These are administrative definitions only — always read the official ClinicalTrials.gov record for study-specific details.

By the Clinical Trials Finder editorial team Guidance last reviewed June 10, 2026 Report an issue

This page does not provide medical advice, eligibility guidance, treatment recommendations, or clinical judgments of any kind.

NCT ID: The unique identifier ClinicalTrials.gov assigns each study. Always starts with “NCT” followed by 8 digits (for example, NCT12345678). Use this ID to look up the official record directly on ClinicalTrials.gov.
Phase 1: An early-stage study type listed on ClinicalTrials.gov, typically involving a small number of participants. The official record on ClinicalTrials.gov contains the full procedural details for any specific study.
Phase 2: A later study type listed on ClinicalTrials.gov, generally involving more participants than Phase 1. See the official ClinicalTrials.gov record for the procedural specifics of any individual study.
Phase 3: A larger comparative study type listed on ClinicalTrials.gov, often comparing an intervention against a control or standard approach across a broader participant group. The official record contains study-specific details.
Phase 4: A post-approval study type listed on ClinicalTrials.gov, conducted after a regulatory decision. The official ClinicalTrials.gov record describes the purpose and design of any specific Phase 4 study.
Early Phase 1: ClinicalTrials.gov’s term for exploratory early studies that precede a traditional Phase 1. The official record on ClinicalTrials.gov contains the procedural details for any specific study assigned this designation.
Study Type: Interventional: A study type classification on ClinicalTrials.gov indicating that the study assigns an intervention (such as a drug, device, or procedure) to participants according to a protocol. See the official record for study-specific design details.
Study Type: Observational: A study type classification on ClinicalTrials.gov indicating that the study observes participants without assigning an intervention. The official ClinicalTrials.gov record describes the observational approach for any specific study.
Recruitment Status: The current enrollment state as listed on the official ClinicalTrials.gov record. Common values include: Not yet recruiting, Recruiting, Active not recruiting, Enrolling by invitation, Completed, Terminated, Suspended, Withdrawn, and Unknown status. Status can change; always check the official record for the current state.
Lead Sponsor: The primary organization listed on ClinicalTrials.gov as responsible for a study. The official record identifies the lead sponsor and their contact information.
Collaborator: An additional organization listed on ClinicalTrials.gov as supporting a study alongside the lead sponsor. The official record lists all collaborators for any specific study.
Protocol: The written plan describing how a study is conducted, including its objectives, design, and procedures. The official ClinicalTrials.gov record may reference or link to the protocol document for a specific study.
IRB / Ethics Review: An independent board that reviews a study protocol to assess ethical conduct before the study begins. The official ClinicalTrials.gov record may note the IRB status or approval for a specific study.
Enrollment (Actual vs. Anticipated): The number of participants enrolled in a study, reported either as an actual count or an anticipated target as listed on the official ClinicalTrials.gov record. Check the official record for the current enrollment figure for any specific study.
Intervention: What the study evaluates, as listed on ClinicalTrials.gov. May include a drug, device, behavioral approach, procedure, dietary supplement, or other category. The official record describes the specific intervention for any individual study.
Condition: The disease, disorder, or health problem that a study addresses, as listed on ClinicalTrials.gov. The official record specifies the conditions for any individual study.
Primary Outcome Measure: The main result that a study is designed to assess, as defined by the study team and listed on ClinicalTrials.gov. The official record contains the full outcome measure description for any specific study.
Eligibility Criteria: The inclusion and exclusion rules defined by the study team and listed on the official ClinicalTrials.gov record. This site does not evaluate whether any individual meets a study’s eligibility criteria — only the study team can make that determination. Always review the official ClinicalTrials.gov record and contact the study team or a qualified healthcare professional for guidance.